1. Field of the Invention
The present invention relates to a driving apparatus for a hybrid vehicle, which is installed in a longitudinal direction of a vehicle body.
2. Description of the Related Art
A parallel system is available as a driving system for a hybrid vehicle that uses an engine and an electric motor as drive sources. In a parallel system, the engine is driven as a main power source for travel, while the electric motor is driven as an auxiliary power source during startup and acceleration. A series system, in which the engine is driven as a power source for power generation and the electric motor is driven as the power source for travel, is also available. Further, a series parallel system combining the series system and the parallel system has been developed. A driving apparatus for these types of hybrid vehicle is constituted by not only an engine, but also a power generation motor driven by the engine, a travel motor coupled to a drive wheel, and so on. When the driving apparatus is installed in a longitudinal direction of a vehicle body, the engine and the power generation motor of the driving apparatus are typically disposed coaxially (see Japanese Unexamined Patent Application Publication No. 2004-330848 and Japanese Unexamined Patent Application Publication No. 2005-35313, for example).
To ensure that power is transmitted from the driving apparatus installed in a longitudinal direction of the vehicle to a front wheel, a differential mechanism is often disposed to the rear of the power generation motor, as in the driving apparatus described in Japanese Unexamined Patent Application Publication No. 2005-35313. However, to secure a space for disposing the differential mechanism, the power generation motor must be designed to be thin. Hence, in a front wheel (four wheel) driving apparatus installed in a longitudinal direction of the vehicle, it is difficult to design the power generation motor such that a core diameter and a core width thereof are substantially identical in order to improve the efficiency of the power generation motor.
Further, to ensure that power is transmitted from the driving apparatus installed in a longitudinal direction of the vehicle to the front wheel, a transfer mechanism may be incorporated into the driving apparatus and a propeller shaft may be disposed so as to extend frontward from the transfer mechanism. However, when a transfer mechanism is incorporated into the driving apparatus, an output shaft of the transfer mechanism must be disposed so as to avoid the power generation motor, which is coaxial with the engine. In other words, the transfer mechanism overhangs greatly in a vehicle width direction from the driving apparatus, and as a result, it may become necessary to modify the shape of a floor tunnel in order to install the driving apparatus in a longitudinal direction of the vehicle body.